In the operation of an internal combustion engine, as in an automotive vehicle, the engine on occasion misfires. This sends a charge of air and gasoline vapors through the exhaust system. This charge tends to collect in the muffler, and when the engine again fires properly, it ignites the vapor mixture resulting in a backfire. During such a backfire, the entire muffler rapidly expands, and then it contracts. After a number of such backfires, the muffler will rupture at its weakest point which in conventional mufflers is normally the connection between one of the muffler end caps and the muffler shell. However, such a rupture can occur at any point on the muffler.
When a muffler so ruptures, the hot exhaust gases can escape therefrom and create a safety hazard. For example, should such a rupture occur near the fuel lines, the hot exhaust gases from the ruptured muffler may be directed toward said fuel lines with the attendant possibility of explosion or fire.
In order to overcome this problem, it has been proposed to employ a muffler having a double outer shell with aligned lockseams extending the length of the shells so that any rupture will occur along the length of those seams. However, in such construction, the connections between the muffler end caps and the shells are strengthened and rigidized to insure that a rupture does not occur at the interconnections between the end caps and shells. The strengthening of these interconnections obviously creates additional manufacturing operations and increases the cost of manufacturing such mufflers.
The instant invention provides a means for controlling the point of rupture in a muffler when it is subjected to a successive number of backfires without substantially increasing the cost of manufacture of the muffler.